Electron discharge device



June 12, 1934.

w. 1.. PARROTT 1,962,969

ELECTRON DISCHARGE DEVICE Filed Feb. 11, 1930 i I Z6 Z6 9 FL g- 4 I u u l8 a? U]T--L- I0 62 a3 .a 24 M 4 4 INVENTOR W. L. PHRROTT ATTOR Patented June 12,

1,992,909 w nmc'raonnrscmnon mmcs QWaI-IeyLawrenoePmothEastOranmNJ wsigner to Westinghouse Lamp Company, aoor- 1 poraflon of Pennsylvania Application February 11, 1930, Serialhlo. 427,478

9 Claims. (cl. ate-am) This invention relates to electron discharge devices \and more particularly to electron discharge devices of the four electrode type wherein is employed a thermionically active hot cathode l of the indirectly heated type, the heater element of which is energized by the passage of an alternating electric current therethrough.

One of the objects of the present invention is to provide a simplified electrode assembly for 1 such devices.

Another object of the present invention is to facilitate the mounting, assembling and manufacture of electron discharge devices of the four electrode type.

Still another object is to provide an electrode assembly for such devices in which the desired predetermined spaced relationship of the electrodes may be substantially maintained throughout assembling, manufacture and during its operating life.

Other objects and advantages will become apparent as the invention is more fully disclosed.

Heretofore in the art-it has been customary to manufacture four electrode electron discharge devices, in which the fourth electrode comprises substantially what is known in the art as a screen grid, which is interposed between the usual control grid electrode and the anode or plate electrode, and,- which during subsequent operation of the device is maintained at a definite electrical potential, depending upon the desired electrical characteristics of the device incorporating the same, for the purpose of controlling or influencing the operating characteristics of the said device.

It has also been customary to employ an indirectly heated type cathode, the heater element of which is energized by alternating electric current. In discharge devices incorporating electrodes concentric with respect to a centrally disposed cathode, it is customary to extend the screen grid electrode in such manner as to substantially enclose the anode electrode, and in such devices it is customary to extend the control electrode lead wire fromthe assembly through the enclosing glass envelope ata point remote from where the remaining electrode lead wires extend through a common press. v

In accordance with the objects of the present invention I have found that the specific electrode assembly of elements that has heretofore been employed, such as for example as is disclosed in my copending application Serial No. 402,559 filed October 26, 1929, entitled Method of manufacturing electron discharge devices, may be l 5 materially simplified and a device having a high degree of uniformity in electrical characteristics obtained by prov ding 'means'for assembling the cathode sleeve member, the control grid and screen grid electrodes into a unit assembly independent or the anode of the device, which unit assembly may thenbe readily mounted into the desired spaced relationship with the anode on the lead wires of the common press of the discharge device, the heater element inserted therein, and the outer enveloping screen grid elements mounted into position in successive operations. By this method of assembly the mounting operation is performed with a minimum of effort and a maximum of efliciency and an electrode assembly obtained thereby which is substantially free from deleterious short circuiting of the electrodes.

'I have found that in the screen grid type of electron discharge device the operating efliciency and the electrical characteristics of the same are primarily dependent upon the proper spacing of the electron emitting cathode surface to the control and inner screen grid electrodes, rather than to the spacing of these electrodes with respect to the plate or anode electrodes. Due to the relatively closer spacing of the cathode, control and screen grid electrodes it requires but relatively slight displacement of either of these electrodes to materially alter the electrical characteristics of the same. It is apparent, therefore, that in 86 the production of relatively large numbers of these devices it is highly essential that the electrical characteristics of the individual devices be substantially identical.

By the present invention I am enabled by, 90 reason of the prior assembly of the cathode, control and screen grid electrodes into a unit assembly having a definite and predetermined spaced relationship, to maintain relatively uniform and consistent electrical characteristics between successive devices of this type when manufacture by machine assembly methods is practiced, a result not heretofore obtained. Moreover by reason of such assembly methods such electrical characteristics are maintained throughout operating life without substantial variation.

Before further disclosing the nature of my invention reference should be made to the accompanying drawing, wherein Fig. 1 is an enlarged side elevational view of an interior screen grid electrode;

Fig. 2 is a view taken along plane 11-11 of the same;

Fig. 3 is an enlarged side elevational view of a control grid electrode;

Fig. 4 is a view taken the same;

Fig. 5 is an enlarged side elevational view of a usual type of cathode sleeve member;

Fig. 6 is a side elevational view of the unit electrode assembly comprising one ofthe features of the present invention;

Flg. 7 is a side elevational view of non-inductive coil type heater element for the indirectly heated cathode shown in Fig. 5;

Fig. 8 is a side elevational view of an electrode assembly with the outer screen grid and plate electrodes cut away showing the position ing of the elements set forth in Fig. 6; and

Fig. 9 is a side elevational view of a completed four electrode radio receiving tube of the 224 type, with the enclosing glass envelope broken away to show the electrode assembly therein.

Referring to Fig. 8 the mount assembly disclosed therein is the same as is employed in receiving tubes of the 224 or screen grid type constructed in accordance with the present invention. The mount assembly comprises essentially a centrally positioned cathode electrode comprised of a heater element 1 which is not shown in this figure but is'set forth specifically in Fig. 7, having terminals 2 and 3 electrically united to lead wires 4 and 5 of press 6, about which heater element is positioned the cathode sleeve member '7, shown in enlarged view in Fig. 5 having an exterior electron emitting coating 8.

concentrically arranged. about the cathode electrode is the control electrode 9, interior screen grid electrode 10, plate electrode 11 and outer screen grid electrode 12 which is electrically connected to the interior screen grid electrode 10 by means of top metal plate 13 and conductor 14 which is united to a common support wire 15 connected to one of the grid posts 28 and by a similar arrangement electrically connecting the other of thescreen grid posts 27 to leading in wire 16. The upper end of screen grid posts 27 and 28 are electrically connected to top metal plate 13 in any convenient manner.

Control electrode 9 is electrically connected to a flexible conductor 17 (Fig. 9) whereby it may be united to a suitable leading in wire extending along. plane Ill-IV of through the enclosing glass envelope 1 8"-"' '(Fig":*9-)

Plate or anode electrode 11 is comprised substantially of a metal cylinder composed of sheet material and is rigidly united to support wire 19 and leading in wire 20 extending through the press 6. The cathode sleeve member 7 is electrically connected by means of flexible metal lead 21 integral with one end thereof to a lead wire 22 supported by crow foot 23, which lead wire extends downwardly in back of and on the exterior of the electrode assembly to connect to leading in wire 24 extending through press 6.

In accordance with my invention this general type of electrode assembly. is simplified by providing a unit assembly of cathode sleeve, control grid, and interior screen grid electrode, which ,may be assembled and put together prior to the mounting operation, which unit assembly provides means therein for positioning the electrodes in direct spaced relationship, which means is independent of subsequent mounting and manufacturing operations, serving to maintain the electrodes in such predetermined desired spaced relationship throughout the entire operating life" pf the device.

Such a unit structure is-obtained by means of spacer members 25 and 26 shown in Figs. 2 and 4, which spacer members engage the grid posts 27, 28 (Fig. 1) and 29, 30 (Fig. 3) in interlocking spaced relationship, and also engage the cathode sleeve member 7 in such manner as to centrally position the sleeve member within the concentrically aligned control and screen grid elements. Such engagement of these electrodes while being substantially rigid as regards subsequent displacement by reason of shocks and strains incident to manufacture, assembly, use, etc., is nevertheless readily assembled and easily dissembled if desired.

Spacer members 25 and 26 are comprised substantially of thin disks of refractory material such as refractory metal oxides, talc, magnesium silicate, or the like materials, preferably such materials which'in the finely powdered or granular form are moldable under pressure to form compressed articles of the approximate desired size,

shape and diameter, and which subsequently may be fired to elevatedtemperatures to sinter the particles together into a substantially rigid structure. It being no part 'of the present invention the process of manufacture of the molded spacer members need not be'further disclosed, it being understood that the openings for engaging the grid posts and cathode sleeve members are preferably moulded therein, as being the more economical procedure.

Heretofore in the art it has been customary to employ an interior screen grid such as is shown in enlarged detail in Fig. 1 which hasa bottom posts 29 and 30 positioned'in the smaller openings when the device is assembled during the manufacturing process.

This method of assembly, however, leaves the upper ends of the grid posts free and unsupported, resulting in variations in the spacings thereof. Moreover the mica disk member is relatively weak and frequently the post members of the control grid are insecurely supported thereon, resulting in total loss of the device by a short circuiting of the electrodes.

In accordance with the present invention the mica disk member is replaced by the thin refractory element 25 which is similar in size, shape and configuration to the mica disk member heretofore employed, and in addition a second refractory spacer member is provided which is substantially identical in size, shape and configuration of the first member, and which is utilized to engage and maintain the upper ends of the grid post members in definite spaced relationship.

The cathode sleeve member is positioned in the central large opening and the unit assembly is then ready to mount upon the supporting lead wires as shown in Fig. 8.

It is customary to initially position the cylindrical-plate or anode electrode upon the leading in and support wires 19 and 20. v

The unit assembly of interior screen grid, control grid, cathode sleeve member and refractory wires 15 and 16. The cathode heater element 1, shown in Fig. '7 which has beenprepared in accordance with the teachings of my copending applications Serial No. 423,935, and Serial No. 423,- 933, filed January 28, 1930, and January 28, 1930, respectively, is next inserted within the cathode sleeve member and the terminals 2 and 3 thereof electrically connected to leading in wires 4 and 5 in the manner shown. The top metal plate section 13 and outer screen grid member 12, comprised of fine wire mesh, are next placed in position and electrically united in the usual manner to each other and to lead support wires 15 and 16.

The control grid 9 and the cathode sleeve member 7 are then electrically connected to lead wires 17 and 22 respectively and the remaining elements of the device such as getter tab 33 placed in position and the mount assembly inserted within an enclosing glass envelope in the usual manner and given the customary manufacturing process of evacuation, seasoning, basing and the like operations.

By reason of this method of assembly a relatively quick mounting of the electrodes is obtained together with an accurate spacing of all the elements, such spacing being substantially identical in all the devices that are manufactured, thereby promoting a high degree of uniformity of product. The spacing of the elements is substantially maintained throughout a relatively long operating life.

It is apparent that whereas I have specifically disclosed the present invention as it may be applied to a radio receiving tube of the so-called screen grid or 224 type, the invention may be equally as well applied to other electron discharge devices of similar type and construction.

It is also apparent that'there may be many modifications of the specific embodiment disclosed herein without departing essentially from the present invention as set forth in the following claims.

What is claimed is:

1. In the manufacture of thermionic discharge devices incorporating an electron emitting cathode, a control electrode, an anode electrode and a screen grid electrode supported substantially from a common stem, the method of mounting said electrodes upon the stem which comprises assembling the cathode, control and screen grid electrodes in concentric spaced relationship in a unit structure independently of said stem and then supporting said structure in concentric spaced relationship to the anode electrode upon said stem.

2. In an electron discharge device of the screen grid type employing an electron emitting unipotential cathode, an independent electrode assembly comprising a cathode, control and screen grid electrodes grouped in concentric definite spaced relationship to each other, said assembly being mounted upon a common stem of the device in spaced relationship to an anode electrode.

3. An electron discharge device comprising a cathode, an anode, control and screen grid electrodes supported in concentric spaced relationship upon a common stem, said cathode, control and screen grid electrodes being grouped in definite concentric spaced relationship as an independent unit structure, said unit structure being positioned on said stem in spaced relationship to said anode electrode.

4. An electron discharge device of the multiple grid type comprising an envelope having a reentrant stem, a tubular anode mounted in said envelope, and an independent electrode assembly mounted on said stem and being in spaced relation to said anode, said electrode assembly comprising a unipotential cathode, a plurality of concentric grid electrodes surrounding said cathode, and means independent of said stem for maintaining said cathode and said grid electrodes in concentric and definite spaced relation to one another.

-5. An electron discharge device of the multiple grid type comprising a stem, an anode, an electron emitting unipotential cathode and an independent electrode assembly mounted on said stem, said assembly including said cathode, a plurality of grids and means for maintaining said grids and cathode in concentric and definite spaced relation to each other, said means having a portion thereof composed of insulating material, with the spacing of said electrodes of said assembly with respect to each other being maintained independently of any leectrode of said assembly being supported by said stem.

6. An electron discharge device of the multiple grid type comprising a stem, an anode, an electron emitting unipotential cathode, and a unitary electrode assembly including said cathode, a plurality of grids and means for maintaining said grids and cathode in concentric and proper spaced relationship with respect to each other, said means including a plurality of supporting posts for said grids and a pair of spaced insulators having openings through which said posts pass and a collar to which are secured two of said posts, said assembly being independent of said anode, the electrodes of said assembly being maintained in said spaced relationship with respect to each other independently of being supported by said stem.

7. An electron discharge device of the multiple grid type comprising a stem, an anode, an electron emitting unipotential cathode, an electrode assembly including said cathode and a plurality of grids, means for maintaining said grids and cathode in concentric and definite spaced relationship with respect to each other, said means including a metallic collar, a plurality of conductors secured to said collar, a plurality of insulators, grid supports and said cathode passing through said insulators, with the spacing of said electrodes of said assembly with respect to each other being maintained independently of any electrode of said assembly being supported by said stem.

8. An electron discharge device of the multiple grid type comprising an envelope, a plurality of lead-in conductors sealed in said envelope, a plurality of grids, an anode and an electron emitting unipotential cathode therein, said electrodes being in concentric and definite spaced relation to each other, means cooperating with two of said grids and said cathode for maintaining said two grids and cathode in definite spaced relationship to each other, said electrodes being electrically connected to said conductors sealed in said envelope, said means, said two grids and said cathode comprising a unitary independent structure whose electrodes remain in said definite spaced relationship to each other independently of any support from said lead-in conductors.

WARLEY LAWRENCE PARRO'I'I'. 

